This invention relates to a memory device which can store data even when a main power source is cut off.
Recently, microprocessors are applied to various control operations, such as for adjustment of a desired temperature and the automatic selection of a television channel. With such control device, it is necessary to store data relating to the control conditions, in a read wirte memory. The read write memory is a volatile memory, therefore, some precautionary measures should be taken in case of momentary power failure. Until now, an auxiliary power source (cell or large capacitor) has been connected to the read write memory in order to retain stored data, thereby carrying out the so-called backup process of preventing stored data from being extinguished even when the main power source is cut off. The period is limited, in which the backup process can be continued by a cell or capacitor. Upon lapse of the period, the contents of the memory disappear. Further, even during the backup period, externally generated noises sometimes change the contents of the memory. Where the contents of a memory disappear or are changed, then the control device which carries out various forms of control in accordance with the memory contents, tends to malfunction. As a result, an unexpected accident happens, depending on the type of object device or instrument whose operation should be controlled. In the case of CPU control, the CPU would give rise to an erroneous results.